Method for angle of arrival determination on frequency hopping air interfaces

ABSTRACT

A method for calibrating an antenna and signal processing system enabling angle of arrival (AOA) determination for a frequency hopping signal, in which a calibration coefficient is determined in response to one or more calibration signals injected into the system at one or more of the frequencies in the hopping sequence and proximate in time to reception of the communication signal. The calibration coefficients are reflective of a frequency and time dependent parameter of a path between the antenna and wireless location sensor. The AOA is determined as a function of the calibration coefficient and the radio frequency energy of the received communication signal. Several embodiment of the method are illustrated.

CROSS REFERENCES

The present application is a continuation application of thenon-provisional application entitled, “ANGLE OF ARRIVAL CALCULATION ONFREQUENCY HOPPING AIR INTERFACES,” application Ser. No. 10/768,687,filed on Feb. 2, 2004, now U.S. Pat. No. 7,379,019 which claims prioritybenefit of provisional application entitled “ANGLE OF ARRIVALCALCULATION ON FREQUENCY HOPPING AIR INTERFACES”, Application Ser. No.60/443,838 and filed on Jan. 31, 2003, the entirety of which is herebyincorporated herein by reference.

The present application is also related to the applications entitled, “AMETHOD FOR CALIBRATING AN AOA LOCATION SYSTEM FOR ALL FREQUENCIES IN AFREQUENCY HOPPING SIGNAL” application Ser. No. 10/768,638 and “A METHODFOR CALIBRATING AN AOA LOCATION SYSTEM FOR FREQUENCY HOPPING AIRINTERFACES” application Ser. No. 10/768,686, each of which are herebyincorporated herein by reference.

BACKGROUND

In the United States, mobile wireless appliance locating equipment isbeing deployed for the purpose of locating wireless callers who dial911. Other services in addition to emergency call servicing arecontemplated and are referred to as location based services (LBS).Wireless location equipment is typical employed as a overlay to wirelesscommunication networks, thus forming a network overlay geo-locationsystem.

In operation, these network overlay location systems take measurementson RF transmissions from mobile appliances at base station locationssurrounding the mobile appliance, and estimate the location of themobile appliance with respect to the base stations. Because thegeographic location of the base stations is known, the determination ofthe location of the mobile appliance with respect to the base stationpermits the geographic location of the mobile appliance to bedetermined. The RF measurements of the transmitted signal at the basestations can include the time of arrival, the angle of arrival, thesignal power, or the unique/repeatable radio propagation path (radiofingerprinting) derivable features. In addition, the geo-locationsystems can also use collateral information, e.g., information otherthan that derived for the RF measurement to assist in the geo-locationof the mobile appliance, i.e., location of roads, dead-reckoning,topography, map matching etc.

Angle of arrival (AOA) is a well-known measurement that can be made onan RF signal for the purpose of locating a mobile appliance operating ina wireless communications network. There have been many methodsdisclosed to produce the AOA. Many of these methods use some method ofcalibration to take into account the dynamic nature of the components inpath prior to the signal measurements made to estimate AOA. In general,the calibration is composed of coupling or injecting a known signalsimultaneously into the receive signal paths at or close to the antennaarray, and measuring the inter-channel characteristics of the testsignal to characterize the traversed components (antenna beam formers,cables, RF distribution units, filters, etc.).

However these methods do not specifically deal with the problems thatarise when the mobile appliance is operating in a wireless network thatutilizes frequency hopping, such as the GSM air interface. The use offrequency hopping in wireless air interfaces is well known, andexemplified by GSM, the most widely deployed air interface in the world,therefore there is a need to address the problems confronted whenlocating frequency hopping mobile appliances.

The current subject matter provides novel approaches for efficientlycalibrating an antenna and signal processing equipment, to allowgenerating accurate AOA measurements in equipment intended to locatewireless mobile appliances operating in a network employing frequencyhopping. The novel approaches includes calibration methodologies andconfigurations.

In order to obviate the deficiencies of the prior art, it is an objectof the current subject matter to present, in a network overlaygeolocation system, a novel improvement in a method for locating amobile appliance. The method including determining the AOA of an uplinksignal from the mobile appliance at a base station from measurements, bya wireless location sensor, of an attribute of the uplink signal and afrequency specific calibration of a path between a multi element antennaarray and the wireless location sensor. The novel improvement, whereinthe uplink signal is a frequency hopping signal and including collectingsegments of a frequency hopping signal associated with each hop andcalibrating the path, at approximately the respective segment's hopfrequency and proximate in time to collecting the respective segments.The improvement also including, estimating the AOA of a frequencyhopping signal from the collected segments and the path calibrations.

It is also an object of the present subject matter to present, in anetwork overlay geolocation system, an improvement to a method forlocating a mobile appliance. The method including determining the AOA ofan uplink signal from the mobile appliance at a base station frommeasurements, by a wireless location sensor, of an attribute of theuplink signal and a frequency specific calibration of a path between amulti element antenna array and the wireless location sensor. The novelimprovement, wherein the uplink signal is a frequency hopping signal andfurther includes collecting segments of a frequency hopping signalassociated with a specific hop; calibrating the path, at approximatelythe specific hop's frequency, proximate in time to the collecting ofeach segment, over a plurality of hopping sequence cycles. Theimprovement also including estimating the AOA of a frequency hoppingsignal from the collected segments associated with the specific hop andthe path calibrations at approximately the specific hop's frequency.

It is still a object of the current subject matter to present, in anetwork overlay geolocation system, an improvement to a method forlocating a mobile appliance. The method including determining the AOA ofan uplink signal from the mobile appliance at a base station frommeasurements, by a wireless location sensor, of an attribute of theuplink signal and a frequency specific calibration of a path between amulti element antenna array and the wireless location sensor. The novelimprovement, wherein the uplink signal is a frequency hopping signal andfurther includes collecting segments of a frequency hopping signalassociated with each frequency hop; calibrating the path, at apredetermined frequency and proximate in time to the collecting of eachof the segments. The improvement also including estimating the AOA of afrequency hopping signal from the collected segments and the pathcalibrations at the predetermined frequency.

It is an additional object of the current subject matter to present, ina network overlay geolocation system, a novel improvement to a methodfor locating a mobile appliance. The method including determining theAOA of an uplink signal from the mobile appliance at a base station frommeasurements, by a wireless location sensor, of an attribute of theuplink signal and a frequency specific calibration of a path between amulti element antenna array and the wireless location sensor. The novelimprovement, wherein the uplink signal is a frequency hopping signal andfurther includes collecting calibration data for each of the hopfrequencies in the frequency hopping sequence; determining arelationship between the calibration data at a selected hop frequencyand the other hop frequencies; collecting segments of a frequencyhopping signal associated with each hop; calibrating the path, at theselected hop frequency and proximate in time to collecting the segmentassociated with each hop. The improvement further including estimatingthe AOA of a frequency hopping signal from the collected segments, thepath calibrations at the selected hop frequency and the determinedrelationship between the calibration data for the selected hop frequencyand the respective hop's frequency.

It is another object of the present subject matter to disclose a novelmethod of calibrating an antenna array and signal processing forreceiving a frequency hopping communication signal. The method includingthe steps of obtaining frequency hopping operational information of thesignal, receiving the signal, and injecting calibration signals atfrequencies of the frequency hopping sequence in response to receipt ofthe communication signal. The method further including determiningcalibration coefficients C₁ and C₂ for said at least two frequencies andapplying C₁ and C₂ to calibrate the antenna and signal processingequipment to a received signal.

It is still another object of the present subject matter to disclose anovel method of calibrating an antenna array and signal processing forreceiving a frequency hopping communication signal. The method includingobtaining frequency hopping operation information of the signal andreceiving the signal. The method injecting a calibration signal at onefrequency of the frequency hopping sequence of the signal in response toreceipt of the signal and determining a calibration coefficient C₁ forthe one frequency and, applying C₁ to a received signal at eachfrequency in the received signal to calibrate the antenna and signalprocessing equipment.

It is yet another object of the present subject matter to disclose anovel method of determining an angle of arrival of a frequency hoppingcommunication signal. The method including obtaining frequency hoppingoperation information of the signal and receiving the signal overmultiple hops of the same frequency. The method including injecting acalibration signal at one frequency of the frequency hopping sequence ofthe signal in response to receipt of signal and determining acalibration coefficient C₁ for said one frequency. The method furtherincludes determining the AOA of the signal based on the hops of thesignal having said one frequency and the calibration coefficient C₁.

It is still yet another object of the present subject matter to disclosea novel method of calibrating an antenna array and signal processing forreceiving a frequency hopping communication signal. The method includingperiodically injecting calibration signals at frequencies in thefrequency band of the system and determining and storing calibrationcoefficients for the frequencies. The method then determinesrelationships relating calibration coefficient of one frequency to thecalibration coefficients of each of the other frequencies using thestored calibration coefficients. The method involves obtaining thefrequency hopping operational information of the signal and receivingsaid signal. The method further includes injecting a calibration signalat one frequency in response to receipt of said signal and determining acalibration coefficient C₁ for said one frequency and, determiningcalibration coefficients for said other frequencies based on thecalibration coefficient for said one frequency and the determinedrelationships. The method includes applying the calibration coefficientscorresponding to the frequencies of the received signal to the receivedsignal.

These objects and other advantages of the disclosed subject matter willbe readily apparent to one skilled in the art to which the disclosurepertains from a perusal or the claims, the appended drawings, and thefollowing detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative system diagram of a system path withcalibration and location components.

FIG. 2 is a flow chart of a method according to an embodiment of thepresent subject matter.

FIG. 3 is a flow chart of a method according another embodiment of thepresent subject matter.

FIG. 4 is a flow chart of a method according still another embodiment ofthe present subject matter.

FIG. 5 is a flow chart of a method according to yet another embodimentof the present subject matter.

FIG. 6 is a flow chart of a method according to an additional embodimentof the present subject matter.

FIG. 7 is a flow chart of a method according to a further embodiment ofthe present subject matter.

FIG. 8 is a flow chart of a method according to a still furtherembodiment of the present subject matter.

FIG. 9 is a flow chart of a method according to yet a further embodimentof the present subject matter.

DETAILED DESCRIPTION

This present subject matter will be described with respect to a GSMnetwork, however the subject matter is applicable and can be applied toa variety of wireless communication networks, and thus is not limited toa GSM network. Thus subject matter of the disclosure will be describewith respect to a network overlay geo-location system that deriveslocation from the uplink signal emitted from a mobile appliance, howeverit is applicable and can also be applied in the context of differentlocation methods, and thus is not limited to the network overlaylocation system described. The selection of the specific network andlocation system is for illustrative purposes only.

The prior art method to determine AOA is to estimate a line of bearingperpendicular to the face of the antenna array based on collecting asegment of RF signal at multiple antenna elements in the array. Eitherjust prior to, or just after the collection of the segment of RF signal,the calibration signal is injected into the path at or near the antennaarray to calibrate the path between the antenna and the signalcollection hardware. The collected calibration data is generally made upof a series of complex voltages for each antenna element, and therelationship between the calibration signal injected into each antennapath is known. The calibration signal is generally at or near the RFfrequency of the signal for which an AOA estimate is to be made. FIG. 1is an illustration of a representative path with multi-element antennaarray 101, a calibration source 102 a for injecting calibration signals(or alternatively calibration source 102 b that transmits thecalibration signal to the antenna), signal processing equipment 103 suchas beam formers, amplifiers or other like equipment and the wirelesslocation sensor 104 that determines the angle of arrival.

The calibration data may include apriori knowledge about the antenna,receiving system and characteristics of the air interface. Thecalibration signal injection must be performed very close in time to thecollection of the signal of interest, and at or very near the same RFfrequency. This is because the characteristics of the path between theantenna and the signal collection functions have dynamic time andfrequency dependent characteristics.

However, in the case of uplink signals that frequency hop, which iswithin the subject matter of the present disclosure, the hop durationsare generally much shorter than the duration of the segment of RF thatmust be collected to produce an AOA estimate. Therefore, multiple RFfrequencies will be contained in the segment of RF that is collected toestimate the AOA using the prior art location methods. Moreover, thehopping occurs with little time spent in the transition from onefrequency to another. Generally, the transition time is insufficient toallow the calibration signal to be injected between hops. Thus theseconditions do not allow the approach of single RF frequency calibrationprior to, or after the signal of interest RF segment collection to beused.

The subject matter of this disclosure presents methodologies andconfigurations to provide path calibration for these circumstances.

In general, the hop RF frequencies, the hopping sequence and time phase,and the hop durations are known apriori. As used in the remainder of thedisclosure frequency hopping sequence includes information regarding oneor more of hopping sequence, hopping duration, phase, and otheroperation parameters of a frequency hopping signal. Several methods thatcan be applied to account for the hopping are described herein:

In one aspect of the subject matter, all of the RF frequencies (f₁ . . .f_(N)) that will be used in the hopping sequence can be calibrated justprior to or just after the segment of RF energy, interchangeablereferred to as RF energy of the received signal or just the receivedsignal, is collected for the signal of interest, emergency call or LBScall. In this aspect each of the frequencies hopped to can be calibratedwith its corresponding calibration data (C₁ . . . C_(N)), where f₁corresponds to C₁, and f₂ to C₂, etc. In this approach The RFcalibration signal injection hardware used in prior art single frequencycases can be utilized, with the only new requirement on the calibrationequipment would be the need for the calibration source to be able totune rapidly through the hop frequencies of the hopping sequence so thatthe calibration can occur rapidly and close (or proximate in time) tothe collection of the RF energy of the signal of interest.

FIG. 2 is an simple flow chart of an embodiment of the present subjectmatter utilizing the above approach to calibrate the signal path fromthe antenna array to the wireless location sensor. In the first step thefrequency hopping sequence of the hopping sequence of the signal (f₁, f₂. . . f_(N)) is obtained from the transmitting mobile over a controlchannel or other network entity of the host network as shown in block201. The mobile's signal which may or may not include communication datais received at the multi-element antenna array as shown in block 203.After receiving the RF energy or received signal, the calibration sourceinjects calibration signals at each frequency of the hopping sequence(f₁, f₂ . . . f_(N)) into the path at or near the antennas as shown inblock 205. The injection of the calibration signal is triggered by thereceipt of the signal of interest. These calibration signals are used todetermine calibration coefficients (C₁, C₂ . . . C_(N)) for each of thefrequencies as illustrated in block 207. With the calibrationcoefficients determined and the signal received the path can becalibrated for each frequency hop of the received signal using thecorresponding calibration coefficients as shown in block 209. Thecalibration coefficients can also be used on a subsequent receivedsignal with the assumption it is received close or proximate to the timethe calibration signal where injected. The calibrated measurements ofthe received signal can know be used to determine the AOA of thetransmitted signal using known methods.

Similarly FIG. 3 is a flow chart of a method in which the injection ofthe calibration signals are not triggered or initiated by the receptionof the signal of interest.

In the first step the frequency hopping sequence of the hopping sequenceof the signal (f₁, f₂ . . . f_(N)) is obtained from the transmittingmobile over a control channel or other network entity of the hostnetwork as shown in block 301. The calibration source injectscalibration signals at each frequency of the hopping sequence (f₁, f₂ .. . f_(N)) into the path at or near the antennas as shown in block 303.The injection of the calibration signal is triggered periodically orupon a measured or anticipated deviation of the accuracy of a systemparameter. These calibration signals are used as above to determinecalibration coefficients (C₁, C₂ . . . C_(N)) for each of thefrequencies as illustrated in block 305. These calibration coefficientsare then stored is a memory device, software or hardware as shown inblock 307 for latter use when a signal of interest in received. A signalis subsequently received at the multi-element antenna array as shown inblock 309 and the calibration coefficients stored in memory are appliedto the received signal to calibrate the received signal to the path orvice versa as shown in block 311.

Another aspect of the disclosed subject matter takes the approach thatcalibration can be done on a single RF frequency either just prior orjust after the signal of interest collection event, and then all RFfrequencies of the hopping sequence can be calibrated with the single RFfrequency. The advantage of this approach is that it is simple and canuse the same calibration equipment as is typically available when singleRF frequency signal are calibrated. The disadvantage of this approach isthat the single calibration frequency most likely will not be completelyaccurate for all of the hopping frequencies, and errors can beintroduced into resultant AOA estimates.

FIG. 4 is an simple flow chart of an embodiment of the present subjectmatter utilizing the above approach to calibrate the signal path fromthe antenna array to the wireless location sensor using only onecalibration signal and calibration coefficient. In the first step thefrequency hopping sequence of the hopping sequence of the signal (f₁, f₂. . . f_(N)) is obtained as shown in block 401. The mobile's signal isreceived at the multi-element antenna array as shown in block 403. Afterreceiving the signal which is a triggering event, the calibration sourceinjects a single calibration signal at a frequency f_(k) selected fromthe frequencies of the hopping sequence (f₁, f₂ . . . f_(N)) into thepath as shown in block 405. The selected frequency can be arbitrarilyselected or can be selected as a function of a statistic of all thefrequencies in the hopping sequence, such as an average, mean, mode,first moment or other statistic of the frequencies in the hoppingsequence. This calibration signal is used to determine a calibrationcoefficient C_(k) for the frequency f_(k) as illustrated in block 407.With the calibration coefficient determined and the signal received, thepath is calibrated for each frequency hop of the received signal usingthe calibration coefficient C_(k) for each frequency as shown in block409. As the calibration varies as a function of frequency it ispreferable to select f_(k) such that it is close the average or the meanof the frequencies (f₁, f₂ . . . f_(N)) or it can also be selected asthe starting or first frequency of the hopping sequence for convenience.

Similarly FIG. 5 is a flow chart of a method in which the injection ofthe calibration signal is not triggered or initiated by the reception ofthe signal of interest. In the first step the frequency hopping sequenceof the hopping sequence of the signal (f₁, f₂ . . . f_(N)) is obtainedfrom the transmitting mobile over a control channel or other networkentity of the host network as shown in block 501. The calibration sourceinjects a single calibration signal at a frequency f_(k) selected asdescribed above from the frequencies of the hopping sequence (f₁, f₂ . .. f_(N)) into the path as shown in block 503. The calibration signal isused to determine a calibration coefficient C_(k) for the frequencyf_(k) as illustrated in block 505. The injection of the calibrationsignal is triggered periodically or upon a measured or anticipateddeviation of the accuracy of a system parameter. This calibration signalis stored as shown in block 507. A signal is subsequently received atthe multi-element antenna array as shown in block 509 and thecalibration coefficient stored in memory is used to calibrate the pathfor the each of the frequencies of the received signal as shown in block511.

Another aspect of the disclosed subject matter illustrates thatdetermining AOA calibration can be done on a single RF frequency eitherjust prior or just after the signal of interest collection event. Thisapproach only collects RF energy from the appliance of interest whenoperating on the frequency used in the AOA calibration. For example, ifthe hopping sequence contains three frequencies f₁, f₂, f₃ and thus thesignal transmitted from the mobile appliance cycles through the sequence(f₁, f₂, f₃, f₁, f₂, f₃, f₁, f₂, f₃ . . . etc.) Therefore if thefrequency selected for the calibration signal is f₂ only the 2^(nd),5^(th), 11^(th) hops will be collected by the WLS, wherein the othermethods show collecting each hop of the received signal. This methodworks well when the total number of RF frequencies in the hopping set issmall and visited in a relatively uniform fashion as demonstrated in theexample. However, in the case of some GSM installations, the number ofRF frequencies in the hopping sequence is 5 or 6, so if one frequency isused from the set, the collection time would have to be increased by afactor of 5 or 6, which may be disadvantageous. The calibrationequipment needed to implement this method can be identical to that usedfor the single RF frequency case.

FIG. 6 is a simple flow chart of an embodiment of the present subjectmatter utilizing the above approach to determine the AOA of a frequencyhopping signal from a mobile appliance which includes calibrating thesignal path between from the antenna array to the wireless locationsensor for the frequency hops having the same frequency using only onecalibration signal and calibration coefficient. In the first step thefrequency hopping sequence of the hopping sequence of the signal (f₁, f₂. . . f_(N)) is obtained as shown in block 601. The mobile's signal isreceived at the multi-element antenna array over multiple hops offrequency f_(k) as shown in block 603. After receiving the signal whichis a triggering event, the calibration source injects a singlecalibration signal at a frequency f_(k) selected from the frequencies ofthe hopping sequence (f₁, f₂ . . . f_(N)) into the path as shown inblock 605. This calibration signal is used to determine a calibrationcoefficient C_(k) for the frequency f_(k) as illustrated in block 607.The calibration coefficient C_(k) is used only to calibrates thefrequency hops having the frequency f_(k). The WLS collects energy fromonly those frequency hops with a frequency f_(k) and along with thecalibration coefficient C_(k) are used to determine the AOA of thereceived signal as shown in block 609.

Similarly FIG. 7 is a flow chart of a method in which the injection ofthe calibration signal is not triggered or initiated by the reception ofthe signal of interest.

FIG. 7 is an simple flow chart of an embodiment of the present subjectmatter utilizing the above approach to determine the AOA of a frequencyhopping signal from a mobile appliance which includes calibrating thesignal path between from the antenna array to the wireless locationsensor for the frequency hops having the same frequency using only onecalibration signal, calibration coefficient and specific frequency hops.In the first step the frequency hopping sequence of the hopping sequenceof the signal (f₁, f₂ . . . f_(N)) is obtained as shown in block 701.The calibration source injects a single calibration signal at afrequency f_(k) selected from the frequencies of the hopping sequence(f₁, f₂ . . . f_(N)) into the path as shown in block 703. Thiscalibration signal is used to determine a calibration coefficient C_(k)for the frequency f_(k) as illustrated in block 705. The calibrationcoefficient C_(k) is used only to calibrates the frequency hops havingthe frequency f_(k) and is stored for latter use as shown in block 707.The mobile's signal is then received at the multi-element antenna arrayover multiple hops of frequency f_(k) as shown in block 709. Thecalibration coefficient C_(k) is used only to calibrates the frequencyhops having the frequency f_(k). The VVLS collects energy from onlythose frequency hops with a frequency f_(k), these hops, along with thecalibration coefficient C_(k) are used to determine the AOA of thereceived signal as shown in block 711.

In an additional embodiment of the disclosed subject matter,periodically, and unrelated to the signal of interest collection times,calibration data can be collected on all of the hopping frequencies.This data can be updated and statistically manipulated to create arunning database of the calibration coefficients (C₁ . . . C_(M)) forall of the frequencies (f₁ . . . f_(M)) of the possible frequencyhopping sequences (f₁ . . . f_(N)) where M≧N. Therefore at any time afrequency hopping signal is received there is a previously determinedcalibration coefficient for each frequency in the frequency hoppingsequence.

FIG. 8 is a simplified illustration of the above embodiment. Thecalibration source injects calibration signals of known frequencies (f₁. . . f_(M)), which represents all the frequencies in the possiblehopping sequences (f₁ . . . f_(N)) into the path as shown in block 801This injection can be periodic or manually initiated. The calibrationsignals are used to determine calibration coefficients (C₁ . . . C_(M))corresponding to the frequencies (f₁ . . . f_(M)) as illustrated inblock 803. These calibration coefficients is also stored in an memorydevice. A signal is subsequently received at the multi-element antennaarray as shown in block 807 and the calibration coefficients stored inthe memory are applied to the received signal to thereby to calibrateeach of the frequencies (f₁ . . . f_(N)) of the received signal to thepath as shown in block 809. The coefficients stored in the database canbe statistically manipulated, to provide averages, weighted averages,mean, median or other statistics such that the particular calibrationcoefficient for a corresponding frequency is a function of more than onecalibration signal at that frequency.

Another embodiment of the disclosed subject matter, periodically, andunrelated to the signal of interest collection times, collectscalibration data on all of the hopping frequencies as previouslydescribe in relation to FIG. 8. This data can then be used to derive arelationship between the calibration data at each of the hoppingfrequencies. For example, if the hopping frequencies are f₁, f₂, f₃ andf₄, then the phase and amplitude of the calibration coefficients C₁, C₂,C₃ and C₄ for each of the antenna elements paths for f₂, f₃ and f₄ canbe referenced to f₁ with a general expression of being C_(x)=F(C_(z),f_(x), f_(z)). In this example C₂=F(C₁, f₂, f₁) and C₃=F(C₁, f₃, f₁).The calibration coefficients for the several frequencies can also bedetermined with a relationship with two or more calibration coefficientsdetermined for two or more reference frequencies, which could begenerally described as C_(x)=F(C_(z), C_(y), . . . C_(N), f_(x), f_(z),f_(y), . . . f_(N)). The premise is that although the calibration maychange over time, the relationship from one frequency to another remainssomewhat constant. Then calibration can be done on a single RF frequencyeither just prior or just after the signal of interest collection event,and the other calibration data could be derived for the remainder of thefrequencies in the hopping set using the single RF frequency calibrationdata and the previously derived relationship between the frequencies.The calibration equipment required to implement this approach would besimilar to that used for the single RF frequency case.

FIG. 9 is a simple flowchart illustrating the above method. Thecalibration source injects calibration signals of known frequencies (f₁. . . f_(M)), which represents all the frequencies in the possiblehopping sequences (f₁ . . . f_(N)) into the path as shown in block 901This injection can be periodic, manually initiated or some otherfrequently occurring trigger. The calibration signals are used todetermine calibration coefficients (C₁ . . . C_(M)) corresponding to thefrequencies (f₁ . . . f_(M)) as illustrated in block 903. Thesecalibration coefficients are used to determine relationships relatingcalibration coefficient of one frequency to the calibration coefficientsof each of the other frequencies using the stored calibrationcoefficients, such as the relationship C_(i)=F(C_(j), f_(i), f_(j))where j=1 to N identifies the reference frequency and i=1 to Nidentifies the frequency who coefficient is to be determined as shown inblock 905. The one frequency to be used as a reference frequency can bearbitrarily selected or can be selected as a function of a statistic ofall the frequencies in the hopping sequence, such as an average, mean,mode, first moment or other statistic of the frequencies in the hoppingsequence.

The relationships exemplified by the functions are also stored in anmemory device. The WLS obtains the frequency hopping sequence of thesignal (f₁ . . . f_(N)) as shown in block 907 and then receives thefrequency hopping signal from the mobile appliance as shown in block909. After receiving the signal which is a triggering event, thecalibration source injects a single calibration signal at a referencefrequency f_(k) as indicated in block 911 and uses the calibrationsignal to determine the calibration coefficient C_(k) a the referencefrequency f_(k) shown in block 913. The method then uses the determinedrelationships or ratios to derive the calibration coefficients (C₁ . . .C_(N)) for each of the remaining frequencies in the frequency hoppingsequence (f₁ . . . f_(N)), such that C_(i)=F(C_(j), f_(i), f_(j)), thus(C₁ . . . C_(N)) becomes (F(C_(k), f₁, f_(k)) . . . F(C_(k), f_(N),f_(k))). The calibration coefficients determined from the relationshipare then applied to the received signal to thereby to calibrate each ofthe frequencies (f₁ . . . f_(N)) of the received signal to the path asshown in block 917.

While preferred embodiments of the present inventive system and methodhave been described, it is to be understood that the embodimentsdescribed are illustrative only and that the scope of the embodiments ofthe present inventive system and method is to be defined solely by theappended claims when accorded a full range of equivalence, manyvariations and modifications naturally occurring to those of skill inthe art from a perusal hereof.

1. In a network overlay geolocation system, a method for locating amobile appliance including determining the AOA of an uplink signal fromthe mobile appliance at a base station from measurements, by a wirelesslocation sensor, of an attribute of the uplink signal and a frequencyspecific calibration of a path between a multi element antenna array andthe wireless location sensor, the improvement comprising the steps of:(a) collecting segments of a frequency hopping signal associated witheach frequency hop; (b) calibrating the path, at a predeterminedfrequency, proximate in time to the collecting of each of the segments;and, (c) estimating the AOA of a frequency hopping signal from thecollected segments and the path calibrations at the predeterminedfrequency.
 2. The method according to claim 1 wherein the predeterminedfrequency is a frequency in the hopping sequence.
 3. The methodaccording to claim 2 wherein the frequency is the starting frequency ofthe hopping sequence.
 4. The method according to claim 1 wherein thestep of calibrating includes generating a calibration signal.
 5. Themethod according to claim 1 wherein the calibrating includes tuning thecalibration source to the predetermined frequency.
 6. The methodaccording to claim 1 wherein the network is a GSM system.